Laser diodes are widely used in projecting and alignment apparatus, such as laser pointers, aligners and leveling equipment. However, the designs of the conventional visible laser diode apparatus have many disadvantages, such as poor thermal dissipation, that present the laser diode from achieving the desired effect in the practical applications.
FIG. 1 illustrates the Light Output Power-Current characteristic of a laser diode. A laser diode will emit laser beam after the operation current exceeds its threshold current I.sub.th. Therefore, only the current above I.sub.th will effect the laser beam, that is, the light output power of a laser diode is proportional to (I.sub.op -I.sub.th), where I.sub.op is the operation current of the laser diode. However, the power consumption is proportional to I.sub.op. Accordingly, as far as the laser beam is concerned, the current under I.sub.th is wasted. In addition, the current below I.sub.th will cause a laser diode to generate heat and thus shorten the lifetime of a laser diode. Furthermore, the operation current is continuously supplied to the laser diode after the laser beam is emitted, thus the laser diode continuously emits laser beam and generates heat. However, the current below I.sub.th does not effect the emission of laser beam but causes the laser diode to generate heat. Therefore, the power consumption of the visible laser diode apparatus is very much and thus the power source (battery) must be replaced frequently. In addition, the lifetime of the laser diode is shortened.